The present invention relates to a magnetic thin-film head with layer-wise build-up on a nonmagnetic substrate for a recording medium which is provided with a magnetizable storage layer, into which information can be written along a track by perpendicular (vertical) magnetization, which magnetic head comprises a ring head-like magnetic conduction body for carrying magnetic flux and having two magnet legs, of which the end pole pieces facing the recording medium are arranged one behind the other as seen in the direction of motion of the head, and having a predetermined small mutual spacing, each having a predetermined small width transversely to the direction of motion, where widening leg parts follow these end pole pieces, and the magnet leg farther removed from the substrate is designed in its widening leg part leading to a greater distance relative to the magnet leg facing the substrate, so that, between the two magnet legs a correspondingly wide space is provided, through which the turns of a write/read coil winding extend. Such a magnetic head is known, for instance, from European Patent Application No. 0,012,912 A1.
The principle of vertical magnetization for storing information is generally known (see, for instance, "IEEE Transactions on Magnetics", Vol. MAG-16 No. 1, January 1980, pages 71 to 76; DE-OS No. 29 24 013 or the mentioned European Patent Application). For this principle, which is frequently also called vertical magnetization, special recording media in the form of rigid magnetic memory discs, flexible individual discs (floppy discs) or magnetic tapes are required. Such a recording medium has at least one magnetizable storage layer of predetermined thickness which contains a magnetically anisotropic material, usually a CoCr alloy. The axis of the so-called easy magnetization of this layer is directed perpendicularly to the surface of the medium. By means of a special magnetic head, the individual pieces of information can be written along a track as bits in successive sections, also called cells or blocks, by which the corresponding magnetization of the storage layer is written in. In practice, the magnetic flux reversals are generally used as information, i.e., the transitions from one direction of magnetization to an opposite one. The bits so obtained have a predetermined extent, also called wavelength, in the longitudinal direction of the track. This extent can be substantially smaller than the limit which is given with the principle of longitudinal (horizontal) storage by demagnetization. Thus, the information density in the recording medium can advantageously be increased according to the principle of vertical magnetization.
The magnetic write- and read heads known for the principle of longitudinal magnetization, i.e., heads by which the write as well as the read function can be executed, however, cannot be adopted directly for use with vertical magnetization. Although, if such heads are used, which in general have a ring-head-like shape, the conduction of the flux to form a circuit closed as far as possible with low magnetic resistance can be obtained also with the flux arrangement desired with the principle of vertical magnetization, it is difficult to generate a sufficiently strong write field at high bit densities and a correspondingly small gap width of the ring head.
One is therefore compelled to develop special magnetic write/read heads for the principle of vertical magnetization. A magnetic head suitable for this purpose, such as shown, for instance, in the European Patent Application mentioned above, has a conduction body of, in particular, ring-head-like shape for conducting the magnetic flux, applied to a nonmagnetic substrate. This conduction body comprises two magnet legs of approximately identical shape, of which the end pole pieces facing the recording medium are arranged one behind the other as seen in the direction of motion and having a predetermined small spacing from each other and each having a small predetermined width. The end pole pieces of these magnet legs change into leg parts which are widened transversely to the direction of motion of the head or transversely to the conduction direction of the magnetic flux, where the magnet head farther removed from the substrate is designed in its corresponding leg part for a greater distance with respect to the magnet leg facing the substrate. In this manner, a sufficiently wide space is obtained between the two magnet legs, through which the turns of a flat write and read coil winding extend. The ring head-like shape of the conduction body is utilized for the write function as well as for the read function of the magnetic head.
The individual parts of this known magnetic head are applied here by thin-film technology on the substrate in layers. This technology is generally known for write/read heads (see, for instance, "Feinwerktechnik und Mestechnik", 88th Year, No. 2, March 1980, pages 53 to 59, or "Siemens-Zeitschrift", Vol. 52, No. 7, 1978, pages 434 to 437).
In the geometric design of the magnet legs of such magnetic heads, the following objectives are pursued, among other things:
The end pole pieces of the magnet legs should be made as thin as possible so that small bit patterns can be read and written. PA1 In addition, a track width as narrow as possible is desired so that in this manner a high area density of the stored information is obtained.
By these requirements, the dimensions of a magnetic head with a shape similar to a ring head, fabricated in thin-film technology, are greatly reduced so that stray fields in the region of the adjacent end pole pieces can lead to short circuits in the magnetic flux. This affects the size of the write fields in front of the pole ends and the reading efficiency adversely. This effect is of importance particularly with the principle of vertical magnetization since with this principle, bit lengths of, for instance, 0.25 .mu.m and track widths of, for instance 10 .mu.m are sought and therefore, the magnetic energy of a bit is correspondingly small.